I n this article I am going to present information
on mycotoxins and spoilage and what they mean to you as a producer. I am
going to talk about the following:

What is the known history of mycotoxins and their seriousness
as a food and feed contaminant

Why , where, and under what conditions mycotoxins are
produced

What practices worsen contamination by mycotoxins

How mycotoxin contamination can be reduced

The future of mycotoxin control and prevention

MYCOTOXINS ARE PRODUCED BY MOLDS

While most fungi only reduce the yield or nutritive
value of the feed they infest, some fungi have the ability to produce toxic
chemicals called mycotoxins. Mycotoxins are complex organic compounds that
are produced by a fungus to increase its virulence as a plant pathogen
by reducing the ability of the plant’s resistance. In contrast, saprophytic
(mold or rot) fungi reduce the competitive ability of other fungi or bacteria
that are competing for the same food source through the release of these
toxins. As these fungi grow, the nutritive value of the plants they infect
or the stored feed they infest is depleted. Available carbohydrates and
other nutrients are converted to carbon dioxide and other fungal metabolites
not readily available as animal nutrients (DiCostanzo). The toxins they
produce have probably been in the environment for millions of years.

When tissue is rotting (spoiling), thousands of bacteria
and fungi are competing for the nutrients in the now dead tissues. Any
fungus that can reduce competition, through production of a toxin, will
become the dominant organism. These toxin-producing fungi did not have
animals in mind as part of their environmental competition. The affect
on animals and humans is purely coincidental due to the similarity of affected
metabolic systems.

Throughout history, the damage due to mycotoxins
has been recorded as ailments and death to humans and animals. Rye and
wheat infected with ergot has caused major human illness due to contaminated
bread with ergotamine. In Europe, Napoleon’s defeat in Russia may not have
been due as much to cold but rather to ergotized grain fed to their animals
which resulted in a catastrophic loss in horses. In England, over 100,000
turkeys were killed (turkey X disease) due to an aspergillus mold in grain
which produced a toxin. Aflatoxin, produced by the fungus Aspergillis,
is one of the most powerful carcinogens known (natural or synthetic). Ten
to 20 parts per billion in the diet of a susceptible animal can cause liver
cancer. This toxin is closely monitored by federal agencies in grain and
peanuts to keep serious levels from reaching the human or animal population.

In Russia, during World War II, thousands of civilians
died due to a fall grain harvest delayed by war until spring. The result
was a grain crop contaminated with T-2 toxin, produced by a Fusarium mold
in the grain heads. T-2 is also the primary toxin in the biological weapon
known as yellow rain. These are only a few of the serious worldwide reports
of toxins causing catastrophic toxicity in humans and livestock (Bullerman).

My own worst experience with a mycotoxin in Vermont
was the toxic reaction of a dairy herd to a mycotoxin contamination in
citrus pulp. Toxicity resulted in the destruction of a100-cow herd over
an eight month period. Major organs were damaged and eventually the entire
herd was destroyed. This type of catastrophic event is highly unusual in
dairy cows with most toxic reactions appearing as poor weight gain, reproduction
problems, reduced feed intake, and reduced milk production.

Many people have asked me if toxin problems in dairy
and other livestock is increasing. My answer to that is yes, I believe
it is. Keep in mind that the dose makes the toxin. Over the past 25 years
we have nearly doubled the intake of the dairy cow, yet we have not doubled
the size of the animal. The significant increase of feed intake of the
dairy cow, which has aided in the major increases accomplished in milk
production, has also caused a significant increase in toxin dosage per
pound of animal when consuming contaminated feeds. Higher intake of toxins,
combined with the increased stress of higher milk production, could account
for the perceived increase in reported mycotoxin problems.

TOXINS OF CONCERN AND THEIR CONDITIONS FOR GROWTH

In the United States, some of the primary toxin producing
fungi found in silage includes Fusarium, Penicillium, and Aspergillus (Shurtleff).
Several toxins of great concern are produced by Fusarium and include vomitoxin
(DON), fumonisin, zearalenone, and T-2. As discussed above, Aspergillus
is known to produce aflatoxin while the fungus Penicillium produces several
serious toxins in silage and other stored feeds. All of these fungus toxins
have been associated with acute, chronic, and sub chronic diseases of livestock.

Various genera of fungi can produce toxins and literally
hundreds (probably thousands) of fungus species have the capacity to produce
toxins. All these fungi have three critical environmental requirements.

temperatures above freezing,

moisture above 20%, and

oxygen.

Limiting any one of these requirements will reduce or
prevent the production of toxins. When considering silage, it is neither
practical nor desirable to limit temperature or moisture. Limiting oxygen
is the key to successfully limiting toxin production during ensilement.
Oxygen is like a light switch. It can turn toxin production on and off
during storage.

Aflatoxin, the most serious carcinogen, has been
found in high levels in peanuts, corn, cotton seed, and grain and can contaminate
milk. This toxin is a serious problem for human and animal health and can
contaminate corn in warmer growing regions. Aflatoxin requires warm ( 85o
F) and moist conditions. Where fall conditions are cool, aflatoxin is rarely
found. For example, in Vermont, our fall conditions are often wet but temperatures
normally average between 50 and 60 degrees. We can find the fungus, Aspergillus,
but the toxin it produces is not produced under our cool conditions. The
further south one goes, the greater the potential of aflatoxin contamination
in corn and other feeds. For those in cool growing regions, however, keep
in mind that aflatoxin can occur in grain shipped in from out of state.
Government and private industry have reputable testing programs to control
the entry of this toxin into the feed and food systems. Always be wary
of special deals from unknown suppliers and be sure to ask about their
mycotoxin testing programs.

In contrast, the fungi in the genus Fusarium produce
their toxins efficiently between 45 and 75 degrees Fahrenheit. This is
just the right temperature for corn, haylage, and silage contamination
in the more northern temperate regions. I don’t know where this group of
fungi would fit in the Florida production with higher temperatures but
Penicillium may fit just fine. Several genera of Fusarium and Penicillium
are known to be plant pathogens and attack corn, grasses, and legumes.
For example, a primary Fusarium disease of corn is ear rot, stalk rot,
and root rot. Corn ears can be infected through the silks at flowering
or through any type of damage such as insect feeding in ears, stalks, or
roots ( Farar). As the fungus grows in the plant tissue, it may or may
not form toxins in high enough levels to cause contamination problems in
feeds. However, a common scenario for high levels of Fusarium toxin infection
in corn starts with wet conditions during silking accompanied by insect
damage (thrips) to silks. The fungus infects the silks directly or through
insect damage and grows down the silks and infects the kernels and cob.
As the season progresses, further damage to the stalk or ear by other pests
such as the European corn borer and birds can result in an increase of
Fusarium rot in damaged tissues. Penicillium rots can also invade through
insect of bird damaged tissues. Rot continues to increase as the season
progresses and toxin production begins to accelerate as the crop begins
to mature (Lepon). The longer corn is allowed to stand in the field after
maturity, the greater the likelihood of significant toxin development.
Levels of Fusarium toxins can be the result of a continuous accumulation
of toxin over time during the growth period and continuing after maturity
and into storage until oxygen becomes limiting or, in the case of grain,
moisture is reduced to less than 20%.

In the case of silage, corn harvested after frost
is at even greater risk of toxin contamination. When the corn is chopped
and placed in a silo, the frosted and now drier silage is difficult to
pack properly. The same could occur in field dried leaves and stems left
too long without frost conditions. The oxygen level in the silo takes longer
to deplete during filling and the fungus can continue to grow and produce
toxin for several days. In one study at the University of Wisconsin (Park),
moldy ear corn increased in toxin concentration by 10 times when left in
contact with air for 8 days after harvest. Our studies in Vermont show
that molded ears left in the field will increase in toxin production significantly
in just two weeks. The level of toxin in cobs was greater than the levels
found in the kernels. Fusarium toxins in corn are probably not reduced
by ensilement (Lepon).

WHICH SILO IS BEST?

At the University of Vermont, eight different mycotoxins
have been found contaminating Vermont feeds including vomitoxin, ochratoxin
A, patulin, penicillic acid, T-2 toxin, verrucarin A, zearalenone, and
kojic acid. These toxins were found to be present (in varying combinations)
in haylage, corn silage, dry hay, grains, and all commodities. In one survey,
the amount of mycotoxin in contaminated silage samples increased as the
ensilement method changed from airtight, upright silos to concrete capped
and uncapped silos. The highest forage concentrations of toxins were found
in horizontal storage methods such as bunker silos and feed piles which
wereleft open to oxygen. In all cases, where greater amounts of
toxins were found, poor management of the upright or bunker silo resulted
in oxygen getting into the stored feed. Well managed bunker silos, covered
with plastic and weighted with tires, had no significantly greater levels
of toxin than well managed upright silos. In any fermentation storage system,
temperature and the presence of moisture is sufficient for toxin production.
But, oxygen will act as the switch which turns toxin production on or off
during storage. In a plastic covered storage system, oxygen penetration
is slowed but not eliminated. The longer the silage is stored, the greater
the opportunity for significant fungus growth and toxin contamination.
In one observation by Trenholm in Canada, the levels of DON increased in
the silo slowly over time even when properly covered.

HOW CAN I MEASURE THE AFFECTIVENES OF MY FORAGE
MANAGEMENT SYSTEM?

Over the past three years we have made more than
1500 tests for Fusarium toxins in all types of silage using a variety of
ensilement methods. The highest levels of toxin are consistently associated
with areas of spoilage. In one survey of 85 farms, 38% of the spoiled areas
in bunker silos tested greater than 3 ppm DON. It is critical that we always
dispose of spoilage as it can contain some of the highest concentrations
of toxin. While DON is not yet shown to cause toxicity in research trials
using pure DON (Charmley), it is the most common Fusarium toxin we find
in Vermont. Approximately 42% of silage tested in Vermont shows positive
for DON, with the majority of samples below 1ppm. However, 15% of the samples
test at above 3ppm. The finding of DON at this level indicates to me that
there may well be some management strategies some farmers can implement
to reduce the threat of toxin development. We used the ELISA DON test as
an indicator to determine if conditions for Fusarium toxin development
have been favorable. Much like the canary in the mine shaft warning miners
of the threat of gas, a high ELISA reading for DON tells us conditions
were favorable for any toxin to develop. This warning encouraged the producer
to take a more critical look at his forage production and storage practices.
We now have numerous anecdotal reports of farmers who have improved management
and gained satisfactory results. This approach was highly successful in
getting farmers to improve storage management practices.

WHAT ABOUT PLASTIC AND OXYGEN PENETRATION?

There is no such thing as an oxygen proof silo. We
would all like to think this is true, but in practical terms our current
technologies are not perfect. When one examines a plastic layer under a
microscope, you will find tiny holes through which oxygen slowly flows.
This is especially true of plastic that is stretched for wrapping bales.
Any damage to the plastic further increases the flow of oxygen from a trickle
to a river and must be repaired as quickly as possible. Our current system
only slows the damage from spoilage over time to an acceptable level until
we can utilize the feed within months of harvest.

WHAT IF I SEE MOLD?

Just as you would not eat moldy food, a good rule
to follow is not to feed moldy hay, haylage, or corn silage to your animals.
There is no way to distinguish between toxic and non-toxic fungi by their
presence in the feed or the discoloration of the feed. The fungi that produce
toxins are present in all feeds since they are naturally occurring in the
fields where the crops are grown. We can see the result of these fungi
when hay is cut and does not dry quickly and rots in the field or in a
wet bail. Fortunately, the presence of these fungi does not automatically
mean toxins are present in the feed. However, the absence of visible molds
does not guarantee that a feed is safe. Dangerous levels of mycotoxins
may accumulate earlier during growth of the crop and often will not be
visible . This level of toxin can then continue to increase during poor
harvest conditions and on into storage. Whenever possible, use the following
adage. "When in doubt, throw it out."

DETOXIFYING CONTAMINATED FEEDS.

Presently there are no economical means to detoxify
contaminated feeds. However, a steady number of dairy consultants and farmers
in Vermont and other states continue to report that the use of sodium bentonite,
and other adsorbent materials, added to feed suspected to be contaminated
with mycotoxin, has resulted in benefits in milk production, feed intake,
and reduced reproductive problems. Sodium bentonite is a complex clay-like
material commonly used as a flow agent to reduce caking in feeds. These
products are mined from ancient deposits of a combination of sea life and
volcanic eruptions. Therefore the purchased ingredient can vary by the
geographical region from which it is obtained. Such materials have been
reported to reduce the harmful affects of aflatoxins in pigs and rats by
binding to the mycotoxin and making it less available for absorption in
the digestive tract (Carson). In dairy cows, there is no direct scientific
evidence to support this claim. However, there is now a large body of anecdotal
reports supporting the use of binding agents. In Vermont, we have observed
a significant number of herds that have benefited by feeding 4 to 8 ounces
of adsorbent when mycotoxin affects were suspected. Increased feed intake
and milk production were sometimes noted within a matter of days. On the
other hand, we have also noted herds with similar symptoms that have had
no beneficial response. The number of adsorbent sources and types do vary
between reporting farms. Thus there can be no general claims made as to
the use of a specific product. However, in practical terms, a local successful
experience may be as good a recommendation as any at this time. We have
also found that if one adsorbent does not work, try another. In specific
cases, up to three products were tried before one was found to work.

CURRENT RESEARCH

The United States Government has placed a high priority
on developing technology to reduce toxin contamination in the food and
feed supply (CAST). Presently there is a flurry of research dealing with
the reduction of aflatoxin in grains and peanuts since it impinges directly
on human health and especially children. Much of this research is devoted
to the development of plant resistance to invasion of Aspergillus and Fusarium
and the cleaning up of grains once contaminated with toxin. There is also
great interest in Fusarium toxins and their control due to their devastating
affect on poultry and pork production. However, dairy production has not
been a high priority for mycotoxin research in this country. Mycotoxin
damage In dairy production is insidious in that it generally causes a sub-acute
or chronic result such as a herd not meeting production expectation of
the managers. In Vermont, several of our herd consultants estimate that
20% of their clients have mycotoxin like problems at any one time and that
almost all farms experience the problem in a 5 year period. Farm losses
can be anywhere from 2 to 10% of milk production. This level of loss is
difficult to measure and pin down to a single cause.

In Europe, there is currently research activity looking
at mycotoxins in both silages and pasture. Both Fusarium and Penicillium
appear to be the major players in silage mycotoxin problems there. In Vermont
we are now concentrating on Penicillium toxins as these are primary spoilage
fungi found in our silages. Other than documenting the presence and toxicity
of such toxins, there is as yet little in the way of new technology to
reduce contamination. However, a lot can be accomplished by using best
storage and harvest management practices available.

In the United States, we need to know at what point
the greatest levels of toxin are being produced in our forages and silages
to efficiently focus our management strategies. This will require the dissection
of the forage management system. We are currently doing just this in Vermont
and looking at environmental and biotic factors involved in increased toxin
contamination.

A major effort currently underway is to develop greater
resistance of corn to ear rot as this is a prime entrance site for infection
and toxin contamination later in storage. We also need increased resistance
in stalk tissue as this represents half the dry weight of silage. In Vermont,
we have shown that stalk tissue contributes up to 50% of DON toxin levels
found in corn silage. Resistance is needed to silk infection as well as
resistance to insect attack through which the fungus can infect the plant.
Some of the newer genetically engineered corn varieties have resistance
to insects such as the European corn borer. Scientists have recently transferred
the gene that produces Bt toxin from the bacterial pathogen to the corn
plant. The bacterial toxin, which is toxic to specific insects, is now
produced by the corn plant to defend against the European Corn Borer. We
are finding that the use of Bt transgenic corn results in decreased corn
borer injury. This has resulted in decreased fungus discoloration in stalks
and ears with a significant reduction in toxin as well.

A CHECK LIST OF PRACTICES WE ADVISE TO PREVENT
TOXIN CONTAMINATION IN SILAGE

Harvest corn and haylage at the recommended maturity
and moisture level for your storage system. DO NOT let corn stand in the
field after completed maturity or killing frost.

Be sure chopper knives are sharp and cutting at the
correct length to improve packing.

Harvest forages as quickly as possible and pack tightly
with the proper weight of tractor matched to the right number of packing
hours and filling rate.

Be sure the silo is sealed to exclude oxygen. Use plastic
cover secured by tires on bunkers.

Patch any holes in plastic covers, bags, or wrapped
bails as soon as possible.

Discard obviously spoiled feed or layers of feed.

Since mycotoxins are highly soluble in water, do not
allow rain to wash through upper layers of spoiled feed.

Clean out leftover feed from feeding bunks regularly.

Consider the use of an inoculant in silage or acid additive
in high moisture corn to enhance fermentation and storageability.

Match the rate of feed removal from the silo face to
the size of the herd. In the north, bunker silo face should be removed
at 4 to 6 inches and upright silo face at 3 to 4 inches per day. Use the
higher rate during the warm seasons.

When confronted with a toxicity problem, stop feeding
the contaminated feed or dilute with a known clean feed.

With your veterinarian or nutritionist, consider the
use of a toxin adsorbent to be mixed with the feed such as sodium bentonite
or a similar material.

Lepon, P, etal. Occurrence of Fusarium species and
their mycotoxins in maize. 7. Formation of DON in a maize plot artificially
inoculated with F. culmorum and the influence of ensilaging on the stability
of DON formed. Archives of animal nutrition. 1990. Volume 40. pp 1005-1012.

This site is maintained by Sid.Bosworth@uvm.edu,
Plant & Soil Science Department, University of Vermont.

Sponsored by:
and

Issued in furtherance of Cooperative
Extension work, Acts of May 8 and June 30, 1914, in cooperation with the
United States Department of Agriculture. University of Vermont Extension,
Burlington, Vermont.University of Vermont Extension and U.S. Department
of Agriculture, cooperating, offer education and employment to everyone
without regard to race, color, national origin, sex, religion, age, disability,
political beliefs, or marital or familial status